Network time reservation cancellation

ABSTRACT

Methods and systems that support, for example, canceling or trimming reservations of a shared communication medium are described. In one embodiment, a method that adapts a network time reservation in a communication network may include, for example, one or more of the following: transmitting a preamble field; transmitting a legacy signal field; transmitting at least one paired field, each paired field comprising a signal field and a protocol data unit; and generating an interframe gap.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

The present application is a continuation of U.S. application Ser. No.11/141,759, filed Jun. 1, 2005, now issued U.S. Pat. No. 7,965,691. SaidU.S. application Ser. No. 11/141,759 makes reference to, claims priorityto and claims benefit from U.S. Provisional Patent Application Ser. No.60/575,950, entitled “Network Time Reservation Cancellation” and filedon Jun. 1, 2004. The above-identified applications are herebyincorporated herein by reference in their entirety.

INCORPORATION BY REFERENCE

The above-referenced United States patent application is herebyincorporated herein by reference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

BACKGROUND OF THE INVENTION

In wireless local area networks (LANs), a network time reservationmechanism is employed to prevent medium access contention that mightotherwise arise due to the inability of all nodes in the network toproperly detect the presence of transmissions from all other nodeswithin the network. This problem is commonly known as the hidden nodeproblem. In the hidden node situation, a hidden node is unable toreceive some or all of the transmission from another node. Thus, thehidden node may incorrectly perceive the network as being in an idlestate when, in fact, the network may be busy. Hidden nodes can be causedby a variety of mechanisms including, for example, distance, presence ofinterference sources, partial rate/modulation incompatibility, noise andother mechanisms. When a hidden node incorrectly determines that thenetwork is idle, the hidden node might attempt its own transmission,thereby causing a collision. While collisions are a natural, acceptablepart of some networks, arising naturally in some methods for arbitratingaccess to the network, collisions are generally not expected to occuronce the arbitration phase of network access has ended. In this regard,hidden nodes and the potential for collisions that hidden nodesintroduce are detrimental to the most efficient operation of thenetwork. To avoid hidden node collisions and the network efficiencylosses created by hidden node collisions, various schemes have beenintroduced including a network reservation mechanism.

However, it may not always be possible to predict, at the time thereservation is requested, the amount of time required to complete thefull set of frame transmissions and/or exchanges. The time can bevariable due to many factors including, for example, incompleteknowledge relating to the number of frames available for transmission inthe sequence when the sequence is initiated (e.g., the availability offrames for transmission may change during the transmission), incompleteknowledge relating to the specific characteristics of the frames thatwill be transmitted during the sequence (e.g., rate and frame lengths),and possible retransmission overhead (e.g., in case of transmissionfailures). Because of the possible lack of ability to predict theexpected duration of the upcoming extended sequence of frametransmissions and/or frame exchanges, the initial reservation may bemade with a conservative value (i.e., inclusive of some time beyond thatwhich might be otherwise necessary), or possibly be made with a fixedvalue, in the case when very little knowledge is known about the numberand length of frames that could be included in the sequence. Such areservation mechanism may, in all likelihood, include more time thannecessary to complete the transmission sequence, resulting in a loss ofefficiency in the use of the communication medium.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of ordinary skill in the artthrough the comparison of such systems and methods with at least someaspects of present invention as set forth in the remainder of thepresent application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

Some embodiments according to some aspects of the present invention mayrelate to the exchange of frames of information (e.g., digitalinformation) using a shared communication medium.

Some embodiments according to some aspects of the present invention mayprovide for canceling and/or trimming a medium reservation in acommunication system that employs a protocol that supports a reservationof a shared communication medium.

Some embodiments according to some aspects of the present invention mayprovide for communicating multiple frames of data in a single mediumaccess.

The above-mentioned embodiments and/or some other embodiments accordingto some aspects of the present invention may be provided, substantiallyas shown in at least one of the figures and/or as described in thespecification, as set forth more completely in the claims.

These and other advantages, aspects, and novel features of the presentinvention, as well as details of illustrated embodiments, thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram illustrating an embodiment of a wirelessdata communication system according to some aspects of the presentinvention.

FIG. 2 illustrates at least some of the fields in an embodiment of aprotocol frame format for use with a shared medium according to someaspects of the present invention.

FIG. 3 illustrates an embodiment of a burst transmission formataccording to some aspects of the present invention.

FIG. 4 shows an embodiment of a burst transmission format according tosome aspects of the present invention.

FIG. 5 shows a flowchart illustrating an embodiment of a method ofoperating a station that exchanges information via a sharedcommunication medium according to some aspects of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Some embodiments according to some aspects of the present inventionrelate to the exchange of frames of information (e.g., digitalinformation) using a shared communication medium.

Some embodiments according to some aspects of the present inventionprovide for canceling and/or trimming a medium reservation in acommunication system that employs a protocol that supports a reservationof a shared communication medium.

Although some references may be made herein with respect to a particularprotocol (e.g., a particular wireless communication protocol), it isunderstood that some embodiments according to some aspects of thepresent invention are not limited to using the exemplary protocolstandards discussed herein. Some embodiments according to some aspectsof the present invention may find application, for example, with othercommunication techniques or with other types of protocols (e.g., othertypes of communication protocols).

Some embodiments according to some aspects of the present inventionprovide a network reservation mechanism that includes, for example, theexchange of a request for a period of network time in which data can besafely exchanged. The request may be followed by the transmission of aconfirmation of the reservation if the reservation is successful. If thereservation is not successful, then no confirmation may be received.Because of the transmission of the confirmation, some of the hiddennodes (e.g., those nodes that were unable to hear the request for thereservation) may be informed of the upcoming transmission, through theirreception of the reservation confirmation. During the reserved timeperiod, the non-participating nodes may not be allowed to make anytransmission attempts, thereby reserving the time for the transmissionby the originally requesting node.

Some embodiments according to some aspects of the present inventionprovide that the reservation time may be used for an extended sequenceof frame transmissions and/or frame exchanges. A method and a systemthat exchanges multiple frames in a single medium access may be found,for example, in U.S. Provisional Patent Application Ser. No. 60/574,109,entitled “Method of Combining Multiple Frames of Data into a SingleMedium Access”, filed on May 25, 2004, and in U.S. patent applicationSer. No. 11/137,689, entitled “Method for Combining Multiple Frames ofData into a Single Medium Access”, filed on May 25, 2005. Theabove-referenced applications are hereby incorporated herein byreference in their entirety.

FIG. 1 shows a block diagram illustrating an embodiment of a wirelessdata communication system 100 according to some aspects of the presentinvention. The communication system 100 may include, for example, afirst station 110, a first legacy station 111, a second station 120 anda second legacy station 121 in wireless communication. In someembodiments according to some aspects of the present invention, at leasta subset of the first station 110, the first legacy station 111, thesecond station 120, the second legacy station 121 are in radio frequency(RF) communication via respective antennas over, for example, a sharedRF communication medium 140. For example, the first station 110 and thesecond station 120 are in radio frequency (RF) communication via a firstantenna 119 and a second antenna 129, respectively. The RF communicationmay occur, for example, over a shared RF communication medium 140. Thestation 110, 120 may convert, for example, transmit signals 115, 125into RF signals to be received by the other station 110, 120. Thestation 110, 120 may convert, for example, the received RF signals intoreceive signals 117, 127. Although four stations are illustrated in FIG.1, some embodiments according to some aspects of the present inventioncontemplate more or less than four stations. In addition, although theantenna 119, 129 is shown as a single antenna coupled to a respectivestation 110, 120, some embodiments according to some aspects of thepresent invention provide that the antenna 119, 120 may comprise one ormore antennas. In some embodiments according to some aspects of thepresent invention, multiple antennas may be used for each of theantennas 119, 120 to support, for example, diversity, beamforming,space-time coded systems or other types of multiple-antenna systems. Theaccuracy of the communication of the transmit signal 115 of the station110 to another station 120 as the receive signal 127 and the accuracy ofthe communication of the transmit signal 125 of the station 120 toanother station 110 as the receive signal 117 may depend upon, forexample, one or more of the following factors: a length of the shared RFcommunication medium 140 between the stations 110, 120; a power level ofthe RF signal transmitted by the stations 110, 120; one or more sourcesof interference along the shared RF communication medium 140; a gainprovided by antennas 119, 129; and one or more factors already known byone of ordinary skill in the art.

In some embodiments according to some aspects of the present invention,the stations 110, 120 are capable of understanding a particular burstformat while the legacy stations 111, 121 may not be capable ofunderstanding the particular burst format.

To communicate data over the shared RF communication medium 140, thestations 110, 120 may employ, for example, a communication protocol. Thecommunication protocol may package, for example, segments of the data tobe communicated into frames. The communication protocol may provide thatadditional information be transmitted for use in, for example, mediumaccess control, error control, and/or control signaling.

FIG. 2 illustrates some of the fields in an embodiment of a protocolframe format 200 for use with a shared medium according to some aspectsof the present invention. The protocol frame format 200 may be similarto or based on, for example, a wireless data protocol as set forth in,for example, IEEE 802.11a or some other protocol. The protocol frameformat 200 may correspond, for example, to the format used for thetransmit signals 115, 127 and/or the receive signals 117, 125. Toprovide an illustrative example, some of the discussions herein relatingto some embodiments according to some aspects of the present inventionmay reference some elements of the IEEE 802.11a physical frame format.Some embodiments of techniques discussed herein may be used, forexample, in IEEE 802.11 networks according to some aspects of thepresent invention. Some embodiments of techniques discussed herein maybe used, for example, in applications in which the frames of acommunication protocol have the same basic structure as that describedherein according to some aspects of the present invention. The protocolframe format 200 is therefore shown for merely illustrative purposes.Other protocols for use over a shared communication medium including,for example, wireless and/or wired communication media protocols arealso contemplated by some embodiments according to some aspects of thepresent invention. The present invention is not limited to use with awireless communication medium and may be applied, for example, to othercommunication media without departing from the spirit and scope of thepresent invention.

In IEEE 802.11a, a physical layer convergence protocol (PLCP) data unit(PPDU) may include, for example, a PLCP header and a PLCP Service DataUnit (PSDU). Physical layer convergence protocol may also be the same asphysical layer convergence procedure. Thus, PLCP may stand for eitherphysical layer convergence protocol or physical layer convergenceprocedure. The PLCP header may carry, for example, information relatingto a method of transmission. The PLCP header may include, for example,information relating to one or more of the following: an encodingmethod, a length and initialization information for a receiver. Theencoding information and length information may be part of, for example,a Signal field 220 of the PLCP header. The initialization informationmay be part of, for example, a Service field 230 of the PLCP header. ThePPDU may be transmitted, for example, by obtaining access to acommunication medium and by transmitting a sequence of bits in aPreamble field 210. The Preamble field 210 may be followed, for example,by one or more symbols (e.g., a single symbol) that encode the Signalfield 220 of the PLCP header. The one or more symbols may be transmittedin a particular robust encoding format. The Signal field 220 symbol maybe followed, for example, by a plurality (e.g., a sequence) of symbolsthat encode the Service field 230 of the PLCP header and the PSDU 230.

Because the wireless medium is a shared medium, each station may attemptto decode the transmitted frames received by that station. A station mayuse the Preamble field 210, for example, to synchronize its datarecovery circuit and/or to determine the channel characteristics betweenthe transmitter and the station. The receiving station may decode theSignal field 220 symbol and may use it to determine a time duration ofthe transmission to follow. In IEEE 802.11a, a station may use thedetection of the Preamble 210 and the information decoded from theSignal field 220 to determine the length of the physical-layer based(e.g., signal-field based) reservation of the shared communicationmedium 140. The length of the reservation may then determine when theshared communication medium 140 may become available for transmissionaccording to the physical-layer based (e.g., signal-field based)reservation mechanism.

As illustrated in FIG. 2, to support the use of the communicationmedium, the protocol frame format 200 may include, for example, a numberof portions or fields as set forth above including, for example, one ormore of the following: the Preamble field 210, the Signal field 220, theService/PSDU field 230 and an Interframe Gap 240, which may also bereferred to as an interframe space. Some embodiments according to someaspects of the present invention may provide that the Interframe Gap 240is not part of the protocol frame format 200, but instead occurs after,for example, a protocol data unit. Some embodiments according to someaspects of the present invention may provide that the Interframe Gap 240is a gap of zero time. Although the Interframe Gap 240 might not containdata, the Interframe Gap 240 may be employed by the stations 110, 120during communication via the shared communication medium. In order forthe communication medium to be shared by a variety of stations 110, 120,portions of the protocol frame format 200 may be transmitted, forexample, at a predefined rate. In some embodiments according to someaspects of the present invention, the Preamble field 210, the Signalfield 220 and the Interframe Gap 240 may be predefined and may betransmitted at a particular data rate (e.g., a known data rate) so as tobe receivable by a variety of receivers. The fields may be of a fixedduration. Other portions or fields of the protocol frame format 200 suchas, for example, the Service/PSDU field 230, which can be used to carrypayload or data, may be transmitted at a different data rate dependingupon, for example, the capabilities of the intended recipient. Throughthe use of, for example, a predefined format and data rate for certainprotocol frame elements or fields, the stations 110, 120 in the wirelessdata communication system 100 may be aware of the operational details ofthe shared communication medium so as to permit the stations 110, 120 toaccess and to utilize the communication medium.

Because particular portions or fields such as, for example, the Preamblefield 210, the Signal field 220 and the Interframe Gap field 240 of theprotocol frame format 200 are of fixed durations, attempts to increasethe throughput of the communication medium may be hampered at times. Insome circumstances; as the data transmission rate over the sharedcommunication medium 140 increases, the Service/PSDU field 230information, for example, shrinks in duration, while the time for theportions or fields of fixed durations (e.g., the Preamble field 210, theSignal field 220, and Interframe Gap portion 240) remains the same.Thus, under some circumstances, a reduction in protocol efficiencyoccurs, for example, as the data rate used for the Service/PSDU field230 increases.

To increase the throughput of a network using a protocol frame formatsimilar to the protocol frame format as illustrated in FIG. 2, it may bedesirable to amortize the overhead of the Preamble field 210 andInterframe Gap portion 240 over a plurality of frames (e.g., over asmany frames being transmitted as possible). If the transmission mediumis very busy or if the transmitted data rates are high, then someembodiments according to some aspects of the present invention providethat a station accumulate a number of frames before it obtains access tothe medium. If the station accumulates a number of frames, then someembodiments according to some aspects of the present invention provide atransmission format that supports the combination of multiple frames ofinformation into a single medium access. In some cases, this mayincrease network efficiency.

FIG. 3 illustrates an embodiment of a compact burst transmission formataccording to some aspects of the present invention. In some embodimentsaccording to some aspects of the present invention, the compact bursttransmission format 300 may include, for example, a Preamble field 310(e.g., a single Preamble field); at least one Signal and Service/PSDUfield pair such as, for example, a plurality of Signal and Service/PSDUfield pairs (320 a, 330 a), (320 b, 330 b), (320 c, 330 c); and anInterframe Gap field 340 (e.g., a single Interframe Gap field). TheSignal fields 320 a-c (e.g., all of the Signal fields) in the compactburst transmission format 300 may be transmitted in a robusttransmission format and rate (e.g., the most robust transmission formatand rate). Using a robust transmission format and rate may increase thelikelihood that the information in the Signal fields 320 a-c is receivedcorrectly by all stations capable of receiving the transmissions fromthe station 110, 120 that is currently transmitting. Each Signal field320 a-c may indicate, for example, the duration of the respectiveService/PSDU 330 a-c portion of the compact burst transmission format300, thereby permitting a receiver to determine the time reserved forthe transmission of the compact burst transmission format 300 using ashared communication medium such as, for example, the shared RFcommunication medium 140. In some embodiments of the compact bursttransmission format 300 according to some aspects of the presentinvention, each Service/PSDU field 330 a-c may be encoded differently.Different encodings may achieve, for example, a minimum transmissiontime and acceptable error rates at the intended receiving station 110,120. The stations 110, 120 (e.g., all or some stations) may attempt todecode the entire compact burst transmission. However, due to randomtransmission errors, varying signal strength, and varying encodingformats, for example, a particular station 110, 120 may not correctlyreceive a particular Service/PSDU 330 a-c. The incorrect reception of asingle Service/PSDU 330 a-c in the burst, however, does not necessarilyaffect adversely the ability of that station to receive the next Signaland Service/PSDU pair in the burst.

FIG. 4 shows an embodiment of a backwards-compatible burst transmissionformat 400 according to some aspects of the present invention. In somecircumstances, it may be desirable to interoperate with stations (e.g.,legacy stations 111, 121) which do not understand the format of compactbursts such as, for example, the compact burst transmission format 300.The use of a backwards-compatible burst transmission format such as, forexample, the backwards-compatible burst transmission format 400illustrated in FIG. 4, may enable legacy stations 111, 121 (e.g., thosestations which are unable to understand the compact burst transmissionformat 300) to determine the medium usage of transmissions using thecompact burst transmission format 300. Some embodiments according tosome aspects of the present invention provide that thebackwards-compatible burst transmission format 400 may be similar (e.g.,almost identical) to the compact burst transmission format 300. However,the backwards-compatible burst transmission format 400 may provide, forexample, a Legacy Signal field 415. In some embodiments according tosome aspects of the present invention, the Legacy Signal field 415 maybe added after the Preamble field 410 (e.g., immediately after thePreamble field 410). The Legacy Signal field 415 may be decoded by, forexample, legacy receivers (e.g., some legacy receivers) and/or receiversthat support, for example, the compact burst transmission format 300.The Legacy Signal field 415 may be adapted, for example, to specify thetime duration of the entire backwards-compatible burst transmissionformat 400.

When a backwards-compatible burst is received at a legacy station suchas, for example, an embodiment of the station 111, 121 according to someaspects of the present invention, the Legacy Signal field 415 may bedecoded by the receiver portion and may specify, for example, theduration of the entire backwards-compatible burst. The legacy station111, 121 may interpret the backwards-compatible burst 400 as a singlelarge frame. Accordingly, the legacy station 111, 121 may not attempt touse the medium at any time during the backwards-compatible burst 400.After the end of the backwards-compatible burst 400, a legacy station111, 121 may then contend for the medium using its normal contentionmechanisms.

When a backwards-compatible burst 400 is received at abackwards-compatible, burst-capable station such as, for example, anembodiment of the station 110, 120 according to some aspects of thepresent invention, the backwards-compatible burst-capable station 110,120 may decode the Legacy Signal field 415 and may store the expectedburst duration. The backwards-compatible burst-capable station then maycontinue to decode the Signal and Service/PSDU pairs (420 a, 430 a),(420 b, 430 b), (420 c, 430 c) as in the compact burst example describedabove with respect to FIG. 3. If any of the Signal fields 420 a-c isdecoded incorrectly, then the station may not contend for thecommunication medium until, for example, the time specified in theLegacy Signal field 415 has elapsed.

Some embodiments according to some aspects of the present inventionprovide a mechanism that cancels, for example, the remaining portion ofa confirmed reservation of a shared communication medium. In someembodiments according to some aspects of the present invention, theconfirmed reservation includes one or more reservations of the sharedcommunication medium (e.g., one or more reservations of the sharedcommunication medium as described above, for example, with respect toFIG. 3, FIG. 4, the PDU-based reservation mechanism and/or theSignal-field-based reservation mechanism).

In some embodiments according to some aspects of the present invention,canceling of the remaining reservation time may be accomplished bysending a specific frame that indicates to the receivers, which havenoted the existing reservation, that the remaining reservation timeshall be cancelled. The reservation may be created when a requestorsends a reservation requesting frame to another network node. Forexample, in a wireless local area network (LAN), a reservationrequesting frame may be sent to an access point (AP). If the reservationrequest frame (e.g., a network reservation request frame) is properlyreceived, then the network node to which the reservation is addressedmay send a reservation confirmation frame back to the reservationrequesting node (provided that no other rule otherwise prevents thereservation from being made). In one embodiment of a reservation requestmechanism according to some aspects of the present invention, the IEEE802.11 protocol provides that the reservation request frame may include,for example, a request-to-send (RTS) frame.

In some embodiments according to some aspects of the present invention,the node (e.g., the owner of the reservation) that sent the originalreservation request and completed its sequence of frame transmissionsand/or exchanges may request that the node that sent the reservationconfirmation, or another node, send a message (e.g., a cancellationrequest indication). The cancellation request may cause the nodes thatreceive the message to cancel any remaining reservation. In someembodiments according to some aspects of the present invention, thereceiving nodes may cancel the remaining reservation upon receipt of thecancellation request indication. In some embodiments according to someaspects of the present invention, the node that sent the reservationrequest and completed its sequence of frame transmissions and/orexchanges may directly transmit a message that causes the nodes thatreceive the message to cancel any remaining reservation.

In some embodiments according to some aspects of the present invention,a LAN frame format includes, for example, a physical layer preamblefollowed by a physical layer header followed by a medium access control(MAC) header, followed by the frame data (e.g., the MAC body orpayload).

In some embodiments according to some aspects of the present invention,at the end of a sequence of frame transmissions and/or frame exchangessent during a period of reservation of the communication medium, aportion of a complete frame, which may be used as a Signaling frame, maybe sent by the holder of the reservation that may include, for example,one or more items (e.g., one of two items). A first item may include,for example, a physical layer preamble, a physical layer header and noMAC fields. The physical layer header may indicate, for example, thatthe MAC portion of the frame is NULL or ZERO length. A second item mayinclude, for example, a physical layer header only in which the physicallayer header indicates that the MAC portion of the frame is NULL or ZEROlength. The NULL- or ZERO-length-indicated MAC frame may signal to thenode which sent the reservation confirmation message that the sendingnode may now send a reservation cancellation message. In someembodiments according to some aspects of the present invention, thephysical layer header might not include, for example, MAC layeraddressing information. The addressing may be implicit or inferred. Forexample, the sending node, which sent the original reservationconfirmation message that is implicitly addressed by the NULL physicallayer header, may send the explicit reservation cancellation frame.

Some embodiments according to some aspects of the present inventionprovide an IEEE 802.11-style wireless LAN. The Signaling frame mayinclude, for example, (1) a physical layer Preamble and a physical layerSignal field or (2) a physical layer Signal field. The reservationcancellation message may include a ZERO-value mechanism such as, forexample, a clear-to-send (CTS) frame with a ZERO-length duration valuein which the duration value is the value of the duration field of theIEEE 802.11 frame.

In some embodiments according to some aspects of the present invention,receivers of the ZERO-value mechanism such as, for example, a CTS framewith ZERO-length duration value may cancel any remaining reservation ofthe shared communication medium upon receipt of the reservationcancellation frame. In some embodiments according to some aspects of thepresent invention, receivers (e.g., in legacy stations) of theZERO-value mechanism might not cancel the remaining reservation of theshared communication medium upon receipt of the reservation cancellationframe.

In some embodiments according to some aspects of the present invention,the receivers of a ZERO-length mechanism such as, for example, a NULL-or ZERO-length frame (e.g., a physical layer Signal field or a physicallayer Preamble plus a physical layer Signal field) may cancel anyremaining reservation upon receipt of this signaling indication.

In some embodiments according to some aspects of the present invention,the transmission of a NULL- or ZERO-length frame may be a reservationcancellation message. If the transmission of a NULL- or ZERO-lengthframe is the reservation cancellation message, then no other messageneed be transmitted to convey the reservation cancellation message inaccordance with some embodiments according to some aspects of thepresent invention.

Some embodiments according to some aspects of the present invention mayuse another mechanism to signal a reservation cancellation. Theparticular node, which originally sent the reservation request messageand, following confirmation of the reservation, sent a sequence of frametransmissions and/or frame exchanges during a period of reservation ofthe medium, may terminate the sequence by sending a new reservationrequest message that includes a ZERO-value mechanism such as, forexample, a reservation request for a duration of ZERO time. Because thereservation request message may include, for example, an explicit MAClayer address, the node sending this frame may send, if it chooses, thereservation cancellation request to any other node. It might not benecessary to send the reservation request message to the node thatconfirmed the earlier, non-zero reservation. In some embodimentsaccording to some aspects of the present invention, the receipt of theZERO-duration reservation request message may be a request to solicitthe reservation cancellation message. Some embodiments according to someaspects of the present invention provide that nodes, which receive theCTS frame with ZERO-length duration value, may cancel any remainingreservation upon receipt of this reservation cancellation frame.

Some embodiments according to some aspects of the present inventionprovide an option such that receivers that receive the ZERO-valuereservation request frame (e.g., an RTS frame as set forth in IEEE802.11) may cancel any remaining reservation.

Some embodiments according to some aspects of the present inventionprovide that the transmission of the NULL- or ZERO-length frame may bethe reservation cancellation message and that no other message need betransmitted.

Some embodiments according to some aspects of the present inventionprovide for tracking multiple reservations by their originatingaddresses. In some circumstances, this may avoid the cancellation ofoutstanding reservations, for example, in adjacent wireless LANs due to,for example, interference and medium sharing. Some embodiments accordingto some aspects of the present invention provide that reservations canbe canceled only when the cancellation message appropriately refers tothe reservation holder. A reference to the reservation holder may bepresent, for example, only in some of the previously mentionedcancellation messages.

Some embodiments according to some aspects of the present inventionprovide that received reservation information from a specific RTSnon-zero value reservation frame and/or received reservation informationfrom a specific CTS non-zero value reservation may be cancelledwhenever, for example, at least one of the following is received: (1) anRTS with the reservation holder indicated as the RTS sender and azero-length duration value and (2) a CTS with the reservation holderindicated as the CTS receiver and a zero-value duration value. Thereservation holder may be identified by the RTS sender address of theoriginal reservation request message and/or by the CTS receiver addressof the original reservation confirmation message.

Some embodiments according to some aspects of the present inventionprovide that stations, which receive an RTS reservation cancellation,rather than completely cancel the reservation time, may instead trim thereservation time to a value (e.g., a smaller value) that is sufficientto allow the reservation cancellation confirmation (e.g., a CTS framewith zero-value duration) to be transmitted.

FIG. 5 is a flowchart illustrating an embodiment of a method ofoperating a station that exchanges digital information via a sharedcommunication medium according to some aspects of the present invention.A station may be, for example, the station 110, 120. In step 512, thestation may begin transmission and may transmit a Preamble portion of abackwards-compatible burst transmission format (e.g., thebackwards-compatible burst transmission format 400) on a sharedcommunication medium (e.g., a shared RF communication medium 140).Although not illustrated in FIG. 5, the action of beginning to transmitmay depend upon detecting that the medium is not currently occupied. Instep 514, the station may determine the duration of the mediumreservation that may be needed to transmit the digital informationavailable (e.g., currently available) at the station for transmission.In step 516, the station may transmit that information as part of aLegacy Signal field in a backwards-compatible burst transmission formatmessage. In step 518 and step 520, the station then begins transmittinga Signal field and PSDU for each of the frames available fortransmission. In query 522, it is determined whether the station hasmore data available for transmission. If more data is available fortransmission, then the process jumps back to step 518 in which thestation transmits the next Signal field of the backwards-compatibleburst transmission format message. If no more data is available fortransmission, then, in query 524, it is determined whether thetransmitted data occupied the entire interval reserved by the LegacySignal field sent earlier in the message, or reserved by the PDU-basedreservation mechanism (e.g., a duration-value mechanism). If theduration of the data frames already transmitted is close enough to theduration signaled in the Legacy Signal field of the message, forexample, close enough to not permit the transmission of a reservationcancellation message, then, in step 526, the station may turn off itstransmitter and may generates an interframe gap, thereby ending thetransmission of the message. If the duration of the data frames alreadytransmitted is not close enough to the duration signaled in the LegacySignal field of the message and, in fact, is substantially shorter thanthe reservation signaled earlier in the Legacy Signal field of themessage, then, in step 530, the station may send a reservationcancellation message. Sending the reservation cancellation message maysignal to other stations using the shared communication medium that themedium is available for use. In step 532, the station may end its use ofthe shared medium by turning off its transmitter and generating anInterframe Gap, thereby ending the process of transmitting the message.Some embodiments according to some aspects of the present inventionprovide that an Interframe Gap is not always generated or is notgenerated. Some embodiments according to some aspects of the presentinvention provide that the Interframe Gap occurs (e.g., only occurs) inthe case of the use of an explicit RTS with zero duration or CTS withzero duration, rather than or in addition to the case in which theSignal field with zero length is used (in which case, the Interframe Gapmight not occur).

Some embodiments according to some aspects of the present inventioncontemplate that the order of the steps and/or queries, for example,illustrated in and/or described in connection with, for example, FIG. 5may be changed or that some steps and/or queries may be added and/orremoved. For example, some embodiments according to some aspects of thepresent invention may provide that, if a reservation is transmittedwithin an RTS/CTS exchange, then the determination of the duration ofthe burst may have been performed before the transmission of anypreamble. Since step 514 may cover, for example, the possibility thatthe duration may be a fixed value that is not necessarily based on thecurrent amount of outstanding data, queries 524 and 522 may be reversedin order. In some embodiments according to some aspects of the presentinvention, it is also contemplated that the total amount of data to betransmitted may change once step 514 has occurred and thus queries 522and 524 may be reversed in order.

Some embodiments according to some aspects of the present invention mayprovide a backwards-compatible burst transmission format such as, forexample, the backwards-compatible burst transmission format 400. Someembodiments according to some aspects of the present invention may useother types of message formats.

Some embodiments according to some aspects of the present invention maybe used, for example, with one or more wireless communication media.Some embodiments according to some aspect of the present invention maybe used with other type so communication media (e.g., wiredcommunication media and wireless/wired communication media).

Some embodiments according to some aspects of the present invention maybe realized in one or more of the following: hardware, software andfirmware. Some embodiments according to some aspects of the presentinvention may be realized in a centralized fashion in at least onecomputer system or in a distributed fashion where different elements maybe spread across several interconnected computer systems. Someembodiments according to some aspects of the present inventioncontemplate using any kind of computer system or other apparatus thathas been adapted to carry out one or more of the systems and/or methodsdescribed herein. Some embodiments according to some aspects of thepresent invention contemplate using a combination of hardware andsoftware that includes, for example, a general-purpose computer systemwith a computer program that, when being loaded and executed, controlsthe computer system such that it carries out one or more of the methodsdescribed herein.

Some embodiments according to some aspects of the present invention maybe embedded in a computer program product that includes, for example,all the features enabling the implementation of one or more of themethods described herein and that, when loaded in a computer system, isable to carry out the one or more methods. In some circumstances, acomputer program may be construed to mean any expression, in anylanguage, code or notation, of a set of instructions intended to cause asystem having an information processing capability to perform aparticular function either directly or after either or both of thefollowing: (1) conversion to another language, code or notation and (2)reproduction in a different material form.

This application makes reference to U.S. Provisional Patent ApplicationSer. No. 60/575,950 filed on Jun. 1, 2004; U.S. Provisional PatentApplication Ser. No. 60/574,109 filed on May 25, 2004; and U.S. patentapplication Ser. No. 11/137,689 filed on May 25, 2005, entitled “Methodfor Combining Multiple Frames of Data into a Single Medium Access”. Theabove-referenced applications are hereby incorporated herein byreference in their entirety.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A communication network, comprising: a firstwireless communication device; a second wireless communication devicethat comprises a legacy station, wherein the first wirelesscommunication device and the second communication device are part of awireless network, wherein the first wireless communication devicetransmits a preamble field, wherein the first wireless communicationdevice transmits a legacy signal field after the preamble field, whereinthe legacy signal field indicates (1) a time duration or (2) a lengthand a rate of at least a backwards-compatible burst transmission,wherein the first wireless communication device transmits a plurality ofpaired fields after the legacy signal field, each paired fieldcomprising a respective signal field and a respective service andprotocol data unit field, wherein the backwards-compatible bursttransmission comprises the plurality of paired fields, wherein thesecond wireless communication device decodes the legacy signal field,wherein the second wireless communication device interprets thebackwards-compatible burst transmission as a single frame, and whereinthe first wireless communication device generates an interframe gapafter the plurality of paired fields.
 2. The communication networkaccording to claim 1, wherein each service and protocol data unit fieldof the plurality of paired fields is encoded differently.
 3. Thecommunication network according to claim 1, wherein the plurality ofpaired fields are decoded if received by a burst-capable station.
 4. Thecommunication network according to claim 1, wherein the legacy signalfield comprises a single legacy signal field.
 5. The communicationnetwork according to claim 1, wherein the legacy signal field relates tothe plurality of paired fields which forms at least a portion of acompact burst.
 6. The communication network according to claim 1,wherein the legacy station or a burst-capable station determines aduration of a reservation of a communication medium.
 7. Thecommunication network according to claim 1, wherein the first wirelesscommunication device generates the interframe gap of zero time.
 8. Thecommunication network according to claim 1, wherein the legacy signalfield can be decoded by the legacy station and a station that supports acompact burst transmission format.
 9. The communication networkaccording to claim 1, wherein a backwards-compatible, burst-capablestation decodes the legacy signal field, and wherein thebackwards-compatible, burst-capable station individually decodes eachpaired field.
 10. The communication network according to claim 1,wherein a remaining reservation time is cancelled if a reservationduration indicated in the legacy signal field has not been substantiallyused.
 11. The communication network according to claim 1, wherein areservation duration is trimmed as indicated in the legacy signal field,or wherein a remaining reservation time is cancelled as indicated in thelegacy signal field.
 12. The communication network according to claim11, wherein the remaining reservation time is cancelled by sending amessage that comprises an indication that a media access control (MAC)portion is of a NULL length or a ZERO length.
 13. The communicationnetwork according to claim 11, wherein the remaining reservation time iscancelled by sending a message that comprises at least one ofrequest-to-send (RTS) frame with a ZERO-length duration value and aclear-to-send (CTS) frame with a ZERO- length duration value.
 14. Thecommunication network according to claim 13, wherein the RTS frame orthe CTS frame comprises information indicating a reservation holder. 15.The communication network according to claim 11, wherein the remainingreservation time is cancelled by sending a message that comprises aNULL-length frame or a ZERO-length frame.
 16. The communication networkaccording to claim 11, wherein the remaining reservation time iscancelled by sending a message that comprises at least one of (1) aphysical layer preamble and a physical layer signal and (2) a physicallayer signal field.
 17. The communication network according to claim 11,wherein the remaining reservation time is cancelled by sending amessage, wherein the message is eceived by a node in the wirelessnetwork that sends a reservation cancellation message to other nodes inthe wireless network.
 18. A wireless communication device, comprising: aburst-capable station in wireless communication with other wirelessstations in a wireless network, wherein the burst-capable stationtransmits, via a plurality of antennas, a legacy signal field and aplurality of paired fields after the legacy signal field, each pairedfield comprising a respective signal field and a respective service andprotocol data unit field, the respective service and protocol data unitfields being encoded differently, the legacy signal field indicating areservation duration that covers at least the transmitting of theplurality of paired fields, wherein a legacy station in the wirelessnetwork decodes the legacy signal field and interprets the plurality ofpaired fields as a single large frame, wherein a burst-capable stationdecodes the paired fields, wherein the burst-capable station generatesan interframe gap after transmitting the plurality of paired fields, andwherein the burst-capable station sends at least one of a ZERO-valueframe, a NULL-value frame, a ZERO-length frame, a NULL-length frame anda ZERO-time reservation request to cancel or to trim the reservationduration.
 19. The wireless communication device according to claim 18,wherein the wireless communication device is backwards compatible, andwherein the wireless communication device supports one or more of thefollowing: diversity, beamforming and space-time coding.
 20. A wirelesscommunication system, comprising: a first wireless communication devicein wireless communication with a second wireless communication device,wherein the first wireless communication device combines multiple framesof data into a single medium access and transmits a burst transmissioncomprising a legacy signal field and a plurality of paired fields, eachpaired field comprising a respective signal field and a respectiveservice and protocol data unit field, the respective service andprotocol data unit fields being encoded differently, the legacy signalfield indicating a reservation duration that covers at least thetransmitting of the plurality of paired fields, wherein the firstwireless communication device generates an interframe gap aftertransmitting the plurality of paired fields, wherein the first wirelesscommunication device transmits a message comprising at least one of aZERO-value frame, a NULL-value frame, a ZERO-length frame, a NULL-lengthframe and a ZERO-time reservation request to cancel or to trim thereservation duration, wherein, if the second wireless communicationdevice includes a legacy station, then the second wireless communicationdevice decodes the legacy signal field and interprets the plurality ofpaired fields as a single large frame, and wherein, if the secondwireless communication device includes a burst-capable station, then thereceiver decodes the paired fields.